feat: generalize some functions in sp-trie (#12376)

* feat: add to_memory_db to StorageProof

* feat: add iter method and generalize iter_nodes

* fmt

* feat: generalize `encode_compact` like `decode_compact`, add to_compact_proof to StorageProof

* fix to_compact_proof

* improve by suggestions

* improve by suggestions

Co-authored-by: Bastian Köcher <[email protected]>